In the production of various construction elements, for instance the A-, B-, and C-columns in a motor vehicle as well as in shock absorbers and their support struts, roof beams, side frame elements, and spring arms it is often desirable for the element to have regions of different thickness. The thicker regions provide strength where needed while the thinner regions make the part as light as possible.
At one time this was most simply accomplished by laminating together metal plates as so-called tailored blanks. Such construction is difficult and delamination is always a problem leading to failure of the part.
Accordingly German 4,231,213 of R. Hansen et al proposes making the part from a flat plate having a starting thickness equal to the thickest part of the finished workpiece. The thick plate is deformed and machined so that its thickness is reduced everywhere except where it needs to be thick. Such a system is difficult because the thin regions of often account for most of the area of the workpiece, so the work reducing all this area to the desired thickness is considerable.
In another system described in German 100 63 040 of H. Knaup a car part is made by compressing a workpiece to form a bump in it, then the workpiece is machined at the bumps to reduce its thickness. Such a system uses a great deal of material, in act reducing much of the workpiece to chips or powder. In addition it requires multiple steps, deforming and machining for instance, to create the desired end product. It is extremely inefficient for the production of a workpiece only a small portion of which needs to be thick.